In recent years, climate changes and frequently occurring disasters, which are presumably attributable to global warming, have had a serious impact on agricultural production, the living environment, energy consumption, and the like. Carbon dioxide in the atmosphere has been of interest as a substance that causes global warming. Examples of carbon dioxide sources include thermal power plants using coal, heavy oil, natural gas, or other fuels; blast furnaces of ironworks where iron oxide is reduced with coke; converters of ironworks where carbon in pig iron is combusted to produce steel; factory boilers; cement plant kilns; and transportation equipment, such as automobiles, ships, and aircraft, using gasoline, heavy oil, light oil, or other fuels. Except for transportation equipment, these carbon dioxide sources are fixed facilities, which are expected to allow easy adaptation to implementation measures for reducing carbon dioxide emissions, and there have thus been attempts to develop methods for separating and recovering carbon dioxide from gases exhausted from these sources.
In addition to the above, attempts have been made to separate and recover carbon dioxide generated, for example, by people breathing and from energy conversion of apparatuses in enclosed spaces, such as deep-submersible vehicles and space stations, and to release the carbon dioxide from the enclosed spaces.
To achieve these objects, the development of a carbon dioxide separating material has been in demand that is capable of stably separating and recovering carbon dioxide and that is capable of repeatedly and continuously separating and recovering carbon dioxide in an efficient manner even under expected conditions of use in a thermal power station and the like (e.g., a carbon dioxide partial pressure of 7 to 100 kPa, 40 to 60° C.) or in a space station and the like (e.g., a carbon dioxide partial pressure of 0 to 1 kPa, 20 to 25° C.). Additionally, from the viewpoint of practical use, the development of a carbon dioxide separating material has been in demand that can downsize a separation and recovery apparatus, and that can be an energy-saving apparatus.
Examples of a method for releasing or recovering carbon dioxide from a carbon dioxide separating material in which carbon dioxide is absorbed include a method for releasing carbon dioxide by heating a carbon dioxide separating material or a container to increase the temperature (a temperature swing method), a method for releasing carbon dioxide by reducing the carbon dioxide partial pressure inside a container containing a carbon dioxide separating material through a depressurizing operation (a pressure swing method), and the like. A carbon dioxide separating material has been in demand that is suitable for any release and recovery method, that absorbs carbon dioxide in a great amount, that achieves a high release rate, that provides a short absorption-release cycle, and that is efficient and highly practical.
As a method for removing carbon dioxide from environmental gas inside a pressurized enclosed space, Patent Literature (PTL) 1 discloses a method for pressurizing the environmental gas and bringing the gas into contact with a dehumidification agent for dehumidification, followed by the removal of carbon dioxide by using a zeolite. However, in the method of PTL 1, which requires dehumidification of the target gas, the gas must be transferred from an enclosed space to a dehumidification tower, then to an absorption tower. This means that downsizing the apparatus is limited.
Patent Literature (PTL) 2 discloses a solid carbon dioxide absorption material in which 2-isopropylaminoethanol is loaded on a support.
Patent Literature (PTL) 3 to 5 disclose a carbon dioxide absorption material that uses a compound having OH or acrylonitrile at one or more of the ends. However, these solid carbon dioxide separating materials aim to solve problems found, for example, in downsizing equipment and in reusing the carbon dioxide separating material. Therefore, a carbon dioxide separating material that achieves a more increased CO2 release amount and a higher CO2 release rate, and that is more efficient and more practical has been in demand.